In
one section there is a large mass, replacing most of the lung lobule,
composed of undulating tubular irregular arrays lined by cuboidal regularly
spaced cells. The lumens of these tubular arrays are distended and
contain necrotic cell debris mixed with mucin and eosinophilic acellular
material.
The neoplastic cells have moderate amounts of cytoplasm with occasional
bright eosinophilic granules or variably sized pale basophilic vacuoles
(mucin). The nuclei are round to oval and basal with occasional prominent
nucleoli and moderate degree of anisokaryosis.
In a small area peripheral to the neoplasm, there are variable numbers
of acidophilic and foamy macrophages.